1. Field of Invention
The present invention relates to an organic light emitting diodes (OLED) pixel structure. More particularly, the present invention relates to an active matrix organic light emitting diodes (AMOLED) pixel structure.
2. Description of Related Art
Display devices employing electroluminescent display elements, such as organic light emitting diodes (OLEDs), have become a popular choice among flat panel displays. OLED displays are used as television screens, computer monitors, portable electronic systems such as mobile phones and personal digital assistants (PDAs). An OLED is a light emitting diode (LED), wherein the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. The emissive electroluminescent layer is situated between two electrodes. Generally, at least one of these electrodes is transparent. An OLED display functions without a backlight. Thus, the OLED display can display deep black levels and can also be thinner and lighter than other flat panel displays such liquid crystal displays (LCDs). OLED displays can use either passive matrix addressing scheme, which is called passive matrix organic light emitting diodes (PMOLED), or active matrix addressing scheme, which is called a (AMOLED). AMOLED is more suitable for higher resolution and larger size displays.
An AMOLED display normally includes a circuit layer formed on a substrate such as glass and an emissive electroluminescent layer formed on the circuit layer. The emissive electroluminescent layer includes a plurality of regularly-spaced pixels positioned in a display area in a form of a matrix with a plurality of rows and a plurality of columns. For color displays, each pixel may further include three sub pixels that emit red, green, and blue (RGB) light, respectively. In this arrangement, each pixel includes three sub pixels arranged as an array in the row direction. Sub pixels of the same color are arranged as continuous stripes in the column direction.
Due to different characteristics of organic light emitting materials of the RGB sub pixels, the RGB sub pixels have light emitting performances, respectively. For example, an AMOLED display may have high brightness but poor color saturation or using high power; other AMOLED display may have broad color field but poor tone; another AMOLED display may have good gamma precision but scarifying the brightness of the AMOELED display.